What are draft classes? What's The Association about?

I've only played NBA Today, MyCareer and Blacktop. I've never tried any other game mode, so I don't know what draft classes are and what they're used for. Can someone also explain The Association as well?

Association, like Dynasty Mode in NBA Live, is a mode in which you can take control of a team and guide them through multiple seasons. You can play or simulate the games, make trades, draft rookies, sign free agents, all that stuff.

A Draft Class is the group of players that is being selected in any given year. For example, LeBron James, Carmelo Anthony, Dwyane Wade and Chris Bosh were drafted in 2003, so they are part of the NBA Draft Class of 2003. NBA 2K's Association Mode allows the creation of custom Draft Classes, so it's possible to create the real upcoming rookies and then draft them when the time comes during an Association game. Otherwise, the game will generate its own Draft Classes with fake players.

Thanks brah.